D.1 Gravitational Fields

Question 1

Newton’s Universal Law of Gravitation

Answer 1

Every single point mass attracts every other point mass with a force that is directly proportional to the product of their masses and inversely proportional to the square of their seperation

Question 2

Point mass

Answer 2

A mass which does not take up any space

Question 3

What two things must be true for Newton’s Universal Law of Gravitation to work?

Answer 3

Both masses will experience the same size force and the objects are point masses if the distance between them is large compared to the physical size of the objects

Question 4

Gravitational fields

Answer 4

A region of space where a mass experiences a force because of it’s mass

Question 5

Gravitational field strength definition

Answer 5

The force per unit mass experienced by a small point mass placed at that point

Question 6

g

Answer 6

Nkg-1 (vector)

Question 7

Combined gravitational fields

Answer 7

Sum of individual field strengths ie g1-g2

Question 8

Orbital motion

Answer 8

Motion of one body around another, following a curved path

Question 9

For an object orbiting another object, the force is

Answer 9

Centripetal force = gravitational force

Question 10

Kepler’s First Law

Answer 10

Planets move on ellipses with the Sun at one foot of the ellipse

Question 11

Perihelion

Answer 11

Closest to the sun

Question 12

Aphelion

Answer 12

Furthest from the sun

Question 13

Major and minor axis

Answer 13

Major is horizontal long, minor is vertical short

Question 14

Kepler’s Second Law

Answer 14

The line joining a planet and the sun sweeps equal areas in equal times (proves that the planet is moving the fastest when it is closest to the Sun)

Question 15

How can you prove that the object is moving fastest at perihelion?

Answer 15

Vp/Va = SA/SP

Question 16

Kepler’s Third Law

Answer 16

The square of the orbital period of a planet is directly proportional to the cube of the semimajor (half of major) axis of the orbit. (PROOF Fc=Fg, mw^2=(GMm/r^2), m^4pi^2r/T^2 = GMm/r^2, r^3=(GM/4pi^2) T^2. G, M, 4, pi are all constant, r^3 prop to T^2)